1. Field of the Invention
The present invention relates to a mobile station equipment used for a radio telephone system installed on vehicles such as automobiles or a radio telephone system including portable radio telephone facilities.
2. Description of the Prior Art
FIG. 1 shows in block diagram the mobile station equipment used for the conventional mobile radio telephone system (e.g., car telephone system). In the figure, indicated by 1 is an antenna, 2 is a transmitter-receiver equipped detachably to the antenna 1, 3 is an RF amplifier connected to the transmitter-receiver 2, 4 is a 1st mixer which is in connection with a frequency synthesizer 13 serving as a 1st local oscillator and constitutes a 1st frequency converting means for converting a radio frequency (RF) reception signal from the RF amplifier 3 into a 1st intermediate frequency (IF) signal, 5 is a band-pass filter connected to the 1st mixer 4, 6 is a second mixer connected to the band-pass filter 5 and constituting a second frequency converting means, 7 is a 2nd local oscillator, e.g., a crystal oscillator, which supplies a local oscillation frequency signal to the 2nd mixer 6 so that it converts the 1st IF signal to a 2nd IF signal, 8 is an IF amplifier connected to the 2nd mixer 6, 9 is a demodulator connected to the IF amplifier 8, 10 is a field strength detector connected to the IF amplifier 8, 11 is a main controller connected to the demodulator 9 and field strength detector 10 and having an audio signal processing function, 16 is a temperature-compensated crystal oscillator (will be termed "TCXO") used for reference frequency generation connected to frequency synthesizer, 12 is a frequency synthesizer connected to the main controller 11 and TCXO 16 and incorporating a sending modulator, 14 is a sending mixer connected to the frequency synthesizer 12 for modulation and frequency synthesizer 13 as a 1st local oscillator, and 15 is a power amplifier connected to the sending mixer 14 and transmitter-receiver 2.
Next, the operation of the above arrangement will be described. The modulating frequency synthesizer 12, with its reference frequency being derived from the TCXO 16, oscillates at a fixed frequency and provides its oscillation output to the sending mixer 14. The frequency synthesizer 13, having a reference frequency provided by the TCXO 16 and serving as a 1st local oscillator, is controlled by a channel setting signal from the main controller 11 and delivers the 1st local oscillation frequency corresponding to the channel to the 1st mixer 4 and sending mixer 14. Accordingly, the frequency synthesizer 12 has its oscillation frequency fixed to the difference between the 1st local oscillation frequency and corresponding transmission frequency, resulting in the equality of the output frequency of the sending mixer 14 to the transmission frequency, and the output of the sending mixer 14 is amplified by the power amplifier 15, processed by the transmitter-receiver 2, and radiated by the antenna 1.
A received radio wave is introduced by way of the antenna 1, transmitter-receiver 2 and RF amplifier 3, and mixed with the output of the frequency synthesizer 13 by the 1st mixer 4 and, after removal of the RF component by the band-pass filter 5, further mixed with the output of the 2nd local oscillator 7 by the 2nd mixer 6. The mixed signal is processed by the IF amplifier 8, and the signal is extracted by the demodulator 9 and then processed by the audio processing function of the main controller 11. A part of the signal at the output of the IF amplifier 8 is also delivered to the field strength detector 10, which provides a voltage representative of the received electric field strength to the main controller 11.
The conventional mobile station equipment for the mobile radio telephone system is arranged as described above, and therefore the frequency stability for reception is dependent on the stability of the TCXO 16 and 2nd local oscillator 7, especially TCXO 16, resulting in a temperature-dependent variation and aging-dependent variation not smaller than around .+-.2 ppm in general. Using, for example a TCXO with a provision of a temperature regulated chamber, with the intention of suppressing the variation as low as .+-.1 ppm, results in an increased cost, bulkiness, start-up time, and power dissipation, and such equipment will be unsuitable for the mobile station of a land mobile telephone system.